The Wait Is Over—ACS Data for Areas with Populations of 20,000 or More

In December 2008, the Census Bureau released the first-ever American Community Survey three-year estimates (this set covers the 2005-2007 time period) for areas with at least 20,000 people. Prior to this, the only ACS data available were for areas meeting a population threshold of 65,000. Table 1 shows the geographic coverage differences between the single-year and three-year estimates for counties, townships, places and school corporations in Indiana.

Table 1: Number of Covered Areas in Indiana by Selected Geography Types for One-Year and Three-Year Estimates

One-Year Estimates

Three-Year Estimates

Counties

25

72

Townships

16

70

Cities and Towns

9

42

School Corporations

24

86

Source: U.S. Census Bureau

Seventy-two Hoosier counties have three-year estimates at their disposal (see Figure 1). The 25 counties meeting the 65,000 population threshold have both single-year and three-year estimates. Twenty counties (those with fewer than 20,000 people) will have to wait until 2010 for the release of the five-year estimates.

Multiyear estimates do not represent one point in time. It is best to think of them as averages over the time period.

If an area has both single-year and multi-year estimates, which one should you choose? It is ultimately a trade-off between currency and reliability, so it will depend on your purpose. The single-year estimate will be more current, but the three-year estimate will have a smaller margin of error (especially important if you are looking at a smaller subset of the population).

Compare apples to apples: that is, you shouldn't compare the 2007 single-year estimate for one geography with the 2005-2007 estimate for another geography.

Rachel Justis, Managing Editor
Indiana Business Research Center, Kelley School of Business, Indiana University